1. Field of the Invention
The present invention relates to a honeycomb regenerator for recovering a waste heat in an exhaust gas by passing the exhaust gas and a gas to be heated alternately therethrough, which is constructed by stacking a plurality of honeycomb structural bodies and especially relates to the honeycomb regenerator used in an exhaust gas having a high temperature or a corrosive exhaust gas having a high temperature.
2. Related Art Statement
In a combustion heating furnace used for an industries such as a blast furnace, an aluminum melting furnace, a glass melting furnace or the like, a regenerator used for improving a heat efficiency, in which a firing air is pre-heated by utilizing a waste heat of an exhaust gas, has been known. As such regenerators, Japanese Patent Laid-Open Publication No. 58-26036 (JP-A-58-26036) discloses a regenerator utilizing ceramic balls, and also Japanese Patent Laid-Open Publication No. 4-251190 (JP-A-4-251190) discloses a regenerator utilizing honeycomb structural bodies.
In the known regenerator mentioned above, at first an exhaust gas having a high temperature is brought into contact with the ceramic balls or the honeycomb structural bodies to store a waste heat of the exhaust gas in the regenerator, and then a gas to be heated having a low temperature is brought into contact with the thus pre-heated regenerator to heat the gas to be heated, thereby utilizing the waste heat in the exhaust gas effectively.
Among the known regenerators mentioned above, in the case of using the ceramic balls, since a contact area between the ceramic balls and the exhaust gas is small due to a large gas-flowing resistivity of the ceramic balls, it is not possible to perform a heat exchanging operation effectively. Therefore, there occurs a drawback such that it is necessary to make a dimension of the regenerator large.
Contrary to this, in the case of using the honeycomb structural bodies, since a geometrically specific surface thereof is large as compared with a volume thereof, it is possible to perform the heat exchanging operation effectively even by a compact body. However, in an actual industrial heating furnace such as a glass melting furnace and a ceramic firing furnace, an operating temperature becomes over 1400.degree. C. Therefore, if a honeycomb regenerator constructed by cordierite honeycomb structural bodies, which are widely used in a field of automobiles as a catalyst carrier, is applied to the heating furnaces mentioned above, the cordierite honeycomb structural bodies become soft and in an extreme case melted. This is because a softening temperature of the cordierite honeycomb structural bodies is about 1400.degree. C. In this case, the honeycomb regenerator cannot be used.
Moreover, in order to improve anti-corrosive properties, a prior art honeycomb regenerator is known, which is constructed by stacking anti-corrosive honeycomb structural bodies and cordierite honeycomb structural bodies. However, the honeycomb regenerator mentioned above cannot be used in a blasting furnace where the temperature reaches about 1300.degree. C. and foreign substances such as an iron scale are included in an exhaust gas. For Example, if use is made of an alumina honeycomb structural body as the anti-corrosive honeycomb structural body, the alumina honeycomb structural body is not reacted with the iron scale, and thus it is no problem. However, in the blasting furnace, an abrupt temperature change occurs during a normal operation. In this case, the alumina honeycomb structural body is susceptible to breakage by the abrupt temperature change mentioned above, since alumina has a high thermal expansion coefficient and a low thermal shock resistance. Further, if the other anti-corrosive honeycomb structural bodies such as mullite, SiC are used, mullite and SiC have a high thermal expansion coefficient, and thus the honeycomb structural bodies are also susceptible to breakage due to an abrupt temperature change as is the same as the alumina honeycomb structural body. Moreover, in order to improve anti-corrosive properties, it is thought that the size of one honeycomb structural body is made small, but in this case a handling operation of the honeycomb regenerator becomes troublesome.
Further, in a heating furnace using a heavy fuel oil, SOx is generated due to a sulfur component included in the heavy oil and is reacts with a water component at a temperature under a dew point of SOx, so that a diluted sulfuric acid is generated. Therefore, if use is made of the cordierite honeycomb structural body in the atmosphere mentioned above, the cordierite honeycomb structural body is corroded.